The cell surface or plasma membrane participates in many processes that are integral to the well-being of the cell, including cellular recognition and adhesion. In addition, plasma membranes of embryonic muscle cells are involved in cell fusion of mononucleated myoblasts to form multinucleated cells which develop into adult muscle fibers. In order to elucidate the molecular mechanism of muscle cell recognition and fusion, it is necessary to have a better understanding of the composition, metabolism and organization of the muscle cell plasma membranes. This proposal deals with the characterization of the protein and glycoprotein of well-defined plasma membrane preparations isolated at various stages of differentiation. In addition, the effect of phospholipase C, an inhibitor or muscle differentiation, on the composition and metabolism of plasma membrane phospholipids will be determined.